Mullah Omar had not been seen in public since the fall of the Taliban regime in 2001

Whether or not Mullah Omar is dead or alive, his long absence from public view is posing a growing threat to the strength of his splintering Afghan Taliban movement.

"Where is Mullah Omar?" is a question sources say is being increasingly and angrily directed at the commander regarded as the acting head, Akhtar Mohammad Mansour.

Commander Mansour has long been reported to be fighting off threats to his authority from more hardline Taliban opposed to any peace talks, including Abdul Qayum Zakir.

The Taliban are also facing a growing challenge from the still small, but increasingly significant presence of the so-called Islamic State in Afghanistan. Videos have emerged of disgruntled Taliban fighters swearing allegiance to the IS's self-declared Caliph Abu Bakr al-Baghdadi.

The Iraqi cleric, who also declared a modern day caliphate in areas under IS control in Iraq and Syria, has publicly mocked the religious and political leadership of Mullah Omar.

Abu Bakr al-Baghdadi, the leader of the Islamic State militia, has ridiculed Mullah Omar's leadership

The so-called p5+1 and Iran agreed a framework deal this month after marathon talks

A historic deal with Iran over its nuclear programme is now within reach - but it's still uncertain whether this rare chance to resolve a major security challenge of our time through diplomacy will be grasped.

This week, the prospect of a final deal, which must be reached by the end of June, could be pulled in two different directions.

About Lyse

Lyse has been reporting for the BBC for nearly 30 years, with posts in Abidjan, Kabul, Islamabad, Tehran, Amman and Jerusalem. In 1999 she joined the BBC's team of presenters but most of her time is spent going back to regions where she lived, and also discovering new ones too.

Lyse often presents from the field for BBC World News, and the BBC World Service's flagship Newshour programme, as well as the News Channel. She works as a correspondent too, reporting across the BBC's global and domestic TV and radio outlets. She also writes for BBC online and posts - judiciously! - on Twitter and Facebook.

Lyse feels at home in many places but is still Canadian. She was educated in Canada, at Queen's University, and the University of Toronto, and has been awarded several honorary doctorates as well as major journalism awards.